busybox: also enable ipv6 support in ifupdown if ipv6 support is enabled

Reported by: Chris Smith <chris.smith@tandberg.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/busybox/busybox.mk

@@ -69,8 +69,10 @@ else
 endif
 ifeq ($(BR2_INET_IPV6),y)
 	$(SED) "s/^.*CONFIG_FEATURE_IPV6.*/CONFIG_FEATURE_IPV6=y/;" $(BUSYBOX_DIR)/.config
+	$(SED) "s/^.*CONFIG_FEATURE_IFUPDOWN_IPV6.*/CONFIG_FEATURE_IFUPDOWN_IPV6=y/;" $(BUSYBOX_DIR)/.config
 else
 	$(SED) "s/^.*CONFIG_FEATURE_IPV6.*/CONFIG_FEATURE_IPV6=n/;" $(BUSYBOX_DIR)/.config
+	$(SED) "s/^.*CONFIG_FEATURE_IFUPDOWN_IPV6.*/CONFIG_FEATURE_IFUPDOWN_IPV6=n/;" $(BUSYBOX_DIR)/.config
 endif
 ifeq ($(BR2_INET_RPC),y)
 	$(SED) "s/^.*CONFIG_FEATURE_MOUNT_NFS.*/CONFIG_FEATURE_MOUNT_NFS=y/;" $(BUSYBOX_DIR)/.config